SXT Status Report November 10, 1998 through November 22, 1998 (Weeks 46-47) D. McKenzie, H. Hudson, N. Nitta SUMMARY Activity diminished a bit as the Leonids came and went. There were no technical problems for Yohkoh or for SXT. SXT conducted some coordinated observations with TRACE and SOHO. SOLAR ACTIVITY The GOES background flux ranged between B and C (see the weekly plots on our "science nugget" Web pages at http://www.solar.isas.ac.jp/sxt_co/index.html). There were four M flares up through Nov. 20, and the largest sunspot groups (NOAA 8375 and 8384) exceeded 600 millionths area. OBSERVING CAMPAIGNS There were no formal coordinate campaign observations during the interval, but we have resumed our close cooperation with SOHO and TRACE whenever possible. TRACE operations continue through the eclipse season. SXT INSTRUMENT STATUS AND CALIBRATION ACTIVITIES The main technical excitement in this period was of course the Leonid meteor storm. Yohkoh took some evasive actions, mainly by turning off the high voltages for two days (but perhaps not during the peak of the storm, which arrived unexpectedly early); SXT continued with normal operations adjusted somewhat for the lack of a flare trigger flag. Activity was low in any case. Full operations of all instruments on Yohkoh have now been resumed successfully. Jean-Pierre Wuelser has now succeeded (in the context of the CDAW described below) in re-working the Yohkoh attitude software to make use of HXA scan data, rather than HXA limb addresses. This was necessitated by the slow changes in the HXA output, which are not understood yet but pose no immediate threat. The attitude results using scan data seem better and more robust than the old system, but a full assessment won't be available until the database for 1997-1998 is rebuilt. In the meanwhile, users should be aware that the some results for events later than mid-1997 may need to be revisited. SXT OBSERVING SEQUENCE TABLES ----------------------------------------------------------------- JST Day UT Time Pass Table ID ================================================================= 09-Nov-98 01:48 UT P2 "981109 P2 ARS1 STD Ver2" 10-Nov-98 00:22 UT P2 "981109 P2 ARS1 DIFF" 10-Nov-98 03:48 UT P4 "981109 P4 ARS1 DARKCAL" 11-Nov-98 00:38 UT P2 "981110 P2 ARS1 STD" 11-Nov-98 23:12 UT P2 "981111 P2 ARS1 STD" 12-Nov-98 23:39 UT P2 "981112 P2 ARS1 STD" 13-Nov-98 23:45 UT P3 "981113 P3 ARS1 STD" 15-NOV-98 22:36 UT P2 981115 P2 ARS1 STD 16-NOV-98 22:52 UT P3 981116 P3 ARS1 DARK+LEO 18-NOV-98 00:52 UT P4 981117 P4 ARS1 STD+LEO 18-NOV-98 20:00 UT P2 981118 P2 ARS1 STD 19-NOV-98 20:16 UT P2 981119 P2 ARS1 DIFF 19-NOV-98 23:42 UT P4 981119 P4 ARS1 STD 20-NOV-98 18:51 UT P2 981120 P2 ARS1 STD+TRACE SCIENCE During Week 46 we conducted the fourth SOHO/Yohkoh CDAW in Palo Alto, or perhaps the first TRACE/SOHO/Yohkoh CDAW. In any case it dealt with assessment of the 3D structure of the coronal active region jointly observed by all three spacecraft during late May and early June. Think for a moment about the technical marvel involved in having three spacecraft at such different locations and velocities observing the same solar arc second simultaneously! See http://diapason.lmsal.com/~cdaw/. The CDAW focused on 3D technical matters (coalignment, modeling, and geometry) rather than physical interpretation. Next March a Medoc workshop will, we hope, make use of the 3D results in actual applications. In brief, this workshop established that two geometrical techniques can be made to work: the "dynamic stereoscopy" approach developed by Markus Aschwanden, and the straight trigonometric approach. With both techniques, at present, we must assume coplanarity of a given loop and that the loop be symmetrical in its plane. Even potential-field modeling, of course, shows non-coplanar and asymmetrical loops, so we hope that between now and the Medoc workshop we will be able to assess the systematic errors resulting from these somewhat restrictive assumptions. We note that potential-field or more complex methods of MHD field modeling also have weaknesses, so that some combination of extrapolations and structure geometry will probably wind up giving the most faithful 3D views of the corona. Please check out the recent weekly science nuggets embedded in the SXT operations reports: 20-Nov-98 Hideous daily difference image 13-Nov-98 Repeated brightening in a flare loop 6-Nov-98 Sideways Ejections The URL's for these and for the full list of science nuggets can be found on http://www.solar.isas.ac.jp/sxt_co/index.html, and the current week is also always kept on http://www.solar.isas.ac.jp/sxt_co/SXTweekly.html. SEMINAR There were no ISAS seminars during this period. OPERATIONS ISSUES No particular issues. VISITORS AND PERSONNEL Phil Shirts and Dick Canfield departed; Nariaki Nitta and Mark Weber arrived. Visitors passing through included Henry Aurass and Lidia van Driel-Gesztelyi. TOHBANS (spacecraft operators) Tohbans for Week 46 SSOC : Shirts, Bargatze(-12), Canfield(+12) KSC : Ohyama, Kasahara SXT_CO: McKenzie SXT_SW: Shirts Tohbans for Week 47 SSOC : Ishii, Ichimoto KSC : Kasahara, Yashiro SXT_CO: McKenzie SXT_SW: Shirts